CORRECTION

A story July 8 misidentified the chemical switch the Durham water utility made at its Brown treatment plant. It stopped using ferric chloride. It started using aluminum sulfate.

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DURHAM -- The city water utility this week stopped using a chemical treatment that is suspected of causing lead to contaminate drinking water in an apartment complex and more than a dozen homes.

The utility abandoned the use of aluminum sulfate at its Brown treatment plant and replaced it with ferric chloride. Both help remove particles, but aluminum sulfate -- known as alum -- might produce fewer chemical contaminants downstream.

Virginia Tech professor Marc Edwards said Durham's switch to alum in 2003 probably altered the ratio of chloride and sulfate in city water. That makes water highly corrosive and likely to leach lead from solder in residential plumbing parts, Edwards said. The EPA requires utilities to limit corrosiveness.

Durham was alerted to lead in water at some city homes in May after a child was diagnosed with lead poisoning. Health officials traced the source to a drinking faucet in an apartment complex where the child had lived. Later tests arranged by the health department turned up lead in apartments and homes nearby.

The city utility intends to retest 11 homes with elevated lead near the complex using its standard protocol, which asks residents to remove aerators from kitchen taps the night before retrieving water samples. But that approach won't duplicate what most people consume after turning on their tap, Edwards has said.

Edwards and the Environmental Protection Agency have found that lead particles trapped in aerators can be the source of lead contamination in water.

"Sampling with the aerator on is more representative of actual consumer exposure, although EPA provides no guidance to utilities on this potentially important issue," Edwards said.

Durham has people remove aerators before the tests because it advises customers to remove and clean them them regularly, utility officials say.